As the second American stricken by Ebola returned to the United States on Tuesday, concern is mounting about the lack of a coordinated international plan to fight the growing outbreak in West Africa.

Nancy Writebol, a missionary from Charlotte, N.C., wore a protective suit as she arrived in Atlanta on Tuesday morning from Liberia. Writebol, 59, was admitted to Emory University Hospital. She will remain in an isolation ward along with Dr. Kent Brantly, a 33-year-old physician from Fort Worth, Texas, who contracted the deadly virus while also treating Ebola patients in Liberia.

The worst Ebola outbreak in history has killed nearly 900 people, mainly in the West African nations of Guinea, Sierra Leone and Liberia, which share a common border.

Ebola only spreads through contact with infected bodily fluids. It cannot be transmitted through airborne particles. But there is no cure or treatment for the virus, which has a death rate of roughly 60 percent.

Both Writebol and Brantly were infected while working at a clinic for Ebola patients in Liberia. Both were part of a missionary response team sponsored by the Christian relief organizations SIM USA and Samaritan’s Purse. Writebol and Brantly remained in serious condition at the hospital on Tuesday after being treated with an experimental drug that has never been tested on humans.

On Wednesday, the World Health Organization will hold a special summit of international experts in Geneva to determine if the outbreak constitutes a “public health emergency of international concern.”

If so, the organization will recommend appropriate temporary measures to reduce the international spread of the disease. That could include mandatory travel restrictions, health screenings for international travelers and other measures.

A collective international response is needed to keep the disease from taking hold in large, densely populated urban areas where it could spread more easily, said Laurie Garrett, senior fellow for global health at the Council on Foreign Relations in New York.

Authorities already fear more infections could develop in Nigeria, where a sick airline passenger who died from the disease wasn’t immediately quarantined. Eight health workers who treated the passenger later showed symptoms of the disease and are now in isolation.

“What will be the global strategy if this virus shows up in Dakkar? In Durbin? In Nairobi? In London? In Paris?” Garrett said. “We have no plan.”

The battle to contain the virus in West Africa is proving difficult for international health organizations, which lack the resources to find, contact and test people who may have had contact with infected patients. The well-being of hundreds of volunteer workers who risk their lives to provide assistance has also become a problem.

Sixty health workers have died during the outbreak, despite precautions such has protective clothing for health care workers, isolation tents for patients and the regular decontamination of clothing and items that entered the patient isolation wards.

“We’re hitting a point where every single health care worker on the ground is exhausted, terrified, burned out,” Garrett said.

The international relief agency Doctors without Borders has issued “plea after plea in recent days to the international community saying, ‘We are exhausted. We are terrified. We want to leave. Can somebody else please come in and take over,’” Garrett said.

Sandra Murillo, a spokeswoman for Doctors Without Borders, said the group has more than 550 staffers in the three affected countries, but the organization has “reached the limits of our capacity on the ground, in terms of the number of experienced people we can send.”

Benoit Matsha-Carpentier, a spokesman with the International Federation of the Red Cross, agreed that more international support is needed, but he said there’s a natural reluctance.

“The fears that we can observe in the (local) communities are being felt at the international level when it comes to deploying,” Matsha-Carpentier wrote in an email. “It is normal, Ebola is a deadly disease, but we also have a duty to help communities who are facing this crisis.”

International Medical Corps, a global humanitarian organization, is sending a team of 10 relief workers to Sierra Leone, but more support is needed, the group said.

“But that doesn’t necessarily mean more people going,” said Sean Casey, who heads the organization’s emergency response in Sierra Leone. “It has to be people with the necessary skills to respond to the outbreak and not put just a lot of people in harm’s way, because it is dangerous.”

Direct Relief, a humanitarian medical aid organization, has sent $400,000 worth of supplies such as medicines and protective equipment to West Africa, said spokeswoman Hannah Rael. But some cargo crews are declining jobs to the affected countries, Rael said.

“We should still be able to get the medical aid there, but we anticipate that this will likely mean the price of transportation will be higher than usual,” she said.

Compounding the difficulty in affected areas is the distrust and suspicion that health workers are facing from residents. Many are refusing to remove ailing family members from their homes, not enforcing quarantines and ignoring calls for safe burials and cremations that limit contact with the infected bodily fluids of corpses.

“Every report I’m getting from the ground has health care workers describing themselves as in a state of fear, even (a state) of siege, feeling that the populations despise and loathe them,” Garrett said.

Local rumors are circulating that volunteer health workers are deliberately infecting people and cutting off their arms and selling the limbs. Others claim that “there are health care workers who are foreign cannibals,” Garrett said.

Many feel the U.S.-Africa Leaders Summit now underway in Washington should focus more directly on the Ebola outbreak, rather than economic development issues. But White House Press Secretary Josh Earnest said an important goal of the meeting is to help people understand that the U.S.-Africa relationship is broad.

“While we stand with our African partners in their time of need, particularly when it comes to something as threatening as an outbreak of a disease like Ebola . . . our relationship is much more diverse and broad than just focusing on that one specific issue,” he said.

Senior White House aides have been briefed regularly on the Ebola crisis, and President Barack Obama has gotten periodic updates as well, Earnest said.

Earnest declined to comment on any specific on-the-ground response. But he did reiterate that the administration, through the Centers for Disease Control and Prevention, has been focused on the virus since March, when initial reports of an outbreak began.

The U.S. Agency for International Development announced Tuesday that it is deploying a team to West Africa to coordinate the government’s response to the outbreak. It will also provide another $5 million to expand programs in Guinea, Sierra Leone and Liberia that help trace people who may be infected and provide health clinics and households with supplies to help prevent the spread of disease.